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GENERAL REPORT OF COMMISSION II
Construction and functioning of plotting instruments and mechanisms;
techniques of measuring photographs and plotting maps; standardization of
tests and quantitative studies of the results obtained.
The report follows a questionnaire addressed to the different national
societies in October 1951. Responses were received from ten countries: Austria,
Belgium, Canada, Finland, Germany, Italy, the Netherlands, Sweden, Switzer-
land, and the United States of America. French experience is, of course, in-
cluded.
I Terrestrial Stereoscopic Photogrammetry.
The reports confirm the tendency already noted during the last Congress;
terrestrial photogrammetry, except in special cases, has ceased to be widely
applied for topography and become a method applied particularly to surveys
on 1 : 1000 scale, for example, of steep valleys for dam sites.
Terrestrial methods are still used in Italy at the Geographic Military
Institute for plotting mountainous regions at Í : 20,000 (map scale 1 : 25,000)
and by the Italian Aero Photogrammetric Survey Company for plans at large
scale for dams, general maps 1 : 2000 to 1 : 5000 and construction plans 1 : 200
to 1 : 500. The first organization employed Santoni photo theodolites with in-
clinable cameras or Zeiss with optical axis horizontal. The EIRA uses a Nistri
photo theodolite model 1951 with an inclinable axis. Base lengths in both cases
are between !/s and 20 of the mean distance plotted. Plotting at the IGM is
done on Santoni Stereocartograph models 3 and 4. Also at the EIRA where a
special corrector for distortion is used to eliminate the distortion of the photo-
graphs. No particular effort is made to keep the axis of the camera horizontal
in this terrestrial photogrammetry; rather merely to take advantage of known
orientation of the plates. The precision given are maximum errors of */10 of a
millimeter for planimetry, + plus or — minus one meter in altimetry for the
maps at 1 : 25,000. For the work of the EIRA the maximum height error is
less than !/10 mm at the scale of the plot; 1 decimeter for 1 : 1000.
Canada employs terrestrial photogrammetry for supplementary control
for plotting aerial photographs. At each geodetic control station photographs
covering the entire horizon are taken. The camera employed was constructed
by the National Research Council; F = 4 inches (102 mm) plates 3%: by
41/, inches (83 X 109 mm). The plates have an infrared emulsion and are
plotted by the Deville graphic method with some modifications. The precision
obtained is ‘/100 of an inch (0.25 mm) in planimetry, 25 feet (7.5 meters) in alti-
metry for 1 : 50,000 scale; 100 feet (30 meters) for the 1 : 250,000.
The United States does not employ terrestrial photogrammetry except to
supplement a triangulation scheme (by the photo alidade). The photographs are
taken with the *transit camera" which is used also for determination of photo-
graphic and horizontal angles.
Germany reports terrestrial photographs taken with the Zeiss phototheo-
dolite (Tan, Taf, Tal) and plotting usually on stereo autographs (Von Orel),
sometimes on Zeiss stereoplanigraphs. The method is used for large scale engi-
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